prepend build flags

Author: Lawrence Nahum

configure.ac

@@ -21,6 +21,7 @@ AM_CONDITIONAL([IS_OSX], [test "x$is_osx" == "xyes"])
 AC_SUBST([LDPATH_VAR])
 
 AM_INIT_AUTOMAKE([foreign subdir-objects])
+: ${CFLAGS="-g"}
 LT_INIT([disable-static])
 
 m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
@@ -140,14 +141,14 @@ if test "x$debug" == "xyes"; then
     fi
 else
     # Optimise and harden if we can
-    AX_CHECK_COMPILE_FLAG([-O2], [AM_CFLAGS="$AM_CFLAGS -O2"])
+    AX_CHECK_COMPILE_FLAG([-O2], [AM_CFLAGS="-O2 $AM_CFLAGS"])
     AC_CHECK_DEFINE([_FORTIFY_SOURCE], [], [
       AX_CHECK_COMPILE_FLAG([-D_FORTIFY_SOURCE=2],
         [CPPFLAGS="$CPPFLAGS -D_FORTIFY_SOURCE=2"])
     ])
     AX_CHECK_COMPILE_FLAG([-fstack-protector-strong], [AM_CFLAGS="$AM_CFLAGS -fstack-protector-strong"])
     AX_CHECK_COMPILE_FLAG([-DNDEBUG=1], [AM_CFLAGS="$AM_CFLAGS -DNDEBUG=1"])
-    AX_CHECK_LINK_FLAG([-O2], [LDFLAGS="$LDFLAGS -O2"])
+    AX_CHECK_LINK_FLAG([-O2], [LDFLAGS="-O2 $LDFLAGS"])
     AX_CHECK_LINK_FLAG([-Wl,-z,relro], [LDFLAGS="$LDFLAGS -Wl,-z,relro"])
 fi